A capping machine or conventional capping apparatus includes a star wheel rotatable about a machine axis and having a plurality of outwardly opening pockets adapted to receive bottles fed in an assembly line fashion to the star wheel. Overlying the rotating star wheel is a plurality of individual capper heads for use in applying a cap to the upper threaded neck of a plastic bottle carried by the star wheel in an arcuate or circular path centered about the machine axis. A turret rotates the star wheel and capping heads in synchronism about the machine axis with an individual capping head located directly above each bottle receiving pocket on the star wheel. The capper heads employ a clutch mechanism whereby the head carrying a cap is rotated and driven axially downwardly at a predetermined force and torque limiting value to tighten the cap onto the bottle neck. In accordance with standard practice, an entrant guide mechanism or conveyor is mated with the capper star wheel to feed filled bottles to an entry point on or end of the path of movement of the capper star wheel. An exit guide mechanism or conveyor is similarly mated to the capper star wheel to transfer the capped bottles from an exit point on or end of the rotating capper star wheel. A stationary rear guide plate extends generally between the entry and exit points on the capping machine and is spaced radially outwardly from the pockets of the star wheel and functions to retain the bottles in the pockets as the star wheel rotates in unison with the capping heads. Below the bottles or containers is a segmented ring, known as a wear plate, rotated with the star wheel onto which the bottles or containers rest during capping. This is a conventional capping machine employed in bottling plants and is the mechanism to which the present invention is directed.
During the capping operation, it is necessary to assure that the bottle does not spin as the cap is tightened. A spinning action during the capping procedure can cause damage to the plastic container and reduce the desired tightness of the cap being applied automatically to the bottle as it is translated in a path determined by the star wheel. In the past, certain cap designs required a relatively high downward force during the capping operation. When this occurs, spinning of the bottle is prevented by frictional contact with the pocket, with the rear guide plate or with both of these structures. As the downward force during the capping operation has been reduced due to the design and functional characteristics of the cap being applied, friction at the neck of the bottles has been increased either by the use of upwardly directed knife ridges provided in the anti-spin segment on the top of the individual star wheel pockets. This structure is disclosed in Peronek U.S. Pat. No. 4,939,890. The knife ridges on the anti-spin segment on each pocket engage the lower surface of a circular flange at the bottom of the threaded neck of a plastic bottle to prevent rotation of the plastic bottle. This type of mechanism was not as effective as the downward force used in the capping operation was decreased due to the changes in design of the cap being applied. For that reason, the anti-rotation or anti-spin device of Peronek U.S. Pat. No. 4,939,890 has become the standard in the trade to prevent rotation of plastic bottles as they are being capped with relatively low downward force. This patent teaches a mechanism for externally applying a downward force on the body of a bottle being capped, which force is independent of the downward force created by the capping operation. This anti-spin or anti-rotation mechanism has been successful; however, it requires a mechanism for exerting a downward force on the bottle which is expensive and is dependent upon certain structural characteristics at the upper portion of the bottle itself. Changes in bottle configuration often require a new force exerting mechanism.
The anti-rotation device of Peronek U.S. Pat. No. 4,939,890 is a successful arrangement for applying plastic threaded safety caps onto the top of plastic bottles where the caps do not require heat to set or position the lower lock band around the neck of the bottle. The lock band of the cap simply snaps into a locking position when the capping head threads the cap onto the upper threaded neck of the plastic bottle. In this type of capping operation, the capper head exerts a downward force of between 15-20 pounds. This low axial force makes retention of the bottle from rotation within the star wheel pocket very difficult. This situation motivated the development and use of the anti-rotation feature disclosed and claimed in Peronek U.S. Pat. No. 4,939,890. The present invention relates to an anti-rotation mechanism to be used on a capping machine, which accomplishes the results of the Peronek anti-rotation arrangement, but does not rely upon developing downward frictional force on the top of the bottle during the capping operation. This concept has been attempted by separating the wear plate from the turret rotating the star wheel so the plate is a fixed arcuate plate under the capping heads onto which a fixed arcuate rib is mounted to engage the bottoms of the bottles as they slide along the plate. This mechanism requires modification of the capping machine and is costly to retrofit.
In accordance with the present invention, there is provided a device or method for preventing rotation of a plastic container, or bottle, of the type having a generally cylindrical body with a circular flange below a threaded neck on the top of the bottle. The invention is particularly applicable for use with a plastic bottle having a pedaloid base, which is somewhat standard in the soft drink industry. These bases include a plurality of downwardly extending pads, generally four or five pads, separated by diverging recesses. In the past, plastic bottles with pedaloid bases have been capped in a standard machine with a lower plate rotated with the capping heads and having contoured recesses or nests directly aligned with the capping heads and pockets of the rotating star wheel. In this prior art arrangement, a plurality of specially contoured recesses that match the pedaloid base configuration are used to receive the bases of the bottles as the bottles are moved by the star wheel. Since the bottles rest upon the lower circular wear plate or ring and are held within a contoured nest on the plate, rotation of the bottles is prevented by an interference between the lower wear plate and the bottom, or base, of the bottle. This arrangement is completely different from the concept of increasing the friction at the top of the bottle or otherwise preventing rotation of the bottle by frictional force. Such structure is now being sold by AMCO Products Company under the trademark Peta Drive. The circular wear plate of this system includes a plurality of upwardly facing recesses, each matching the lower pedaloid base of the bottles. The bottles rest on the lower wear plate as it rotates with the star wheel. Physical interference prevents rotation of the individual bottles. Provision of a lower circular wear plate with machined recesses, each matching the contour of a pedaloid base of the plastic bottles, is quite expensive. Each of the contoured recesses must be specially produced and accurately matched with respect to the actual shape of each pedaloid base of the bottle being processed. Consequently, each bottle required its own lower support wear plate. Indeed, when the filled bottles being capped are changed from a four pad pedaloid base to a five pad pedaloid base, a completely new, specially machined plate for supporting the pedaloid bases must be assembled onto the machine. This arrangement for providing a plate rotatable with the star wheel for supporting the lower pedaloid bases of the bottles demands a plate which must be accurately machined for use with specific star wheels.
Another anti-rotation system includes arrangement for fixing the support member or wear plate in a position spaced from the turret where the containers slide along a rib as the container is moved around the arcuate path dictated by the movement of capping head and the star wheel. The rib extends into the lower recess of the pedaloid base of the individual bottle to prevent rotation of the bottle or container as the capping head drives the cap onto the upper threaded neck of the bottle. By using this construction, a lower support plate carrying the upstanding rib is fixed and does not rotate with the star wheel. The upwardly extending rib prevents rotation of the bottles during the capping operation. This use of a fixed rib constitutes an improvement over other arrangements for using a lower plate with specially contoured recesses to provide interference against rotation of the bottle by the capping head; however, it requires a modification of the capping machine and is expensive to retrofit.